Step drill bit

ABSTRACT

A step drill bit includes a shank and a body having a proximal end adjacent the shank and a distal end opposite the proximal end. The body defines a plurality of axially stacked, progressively sized steps including a first step at the distal end, a terminal step at the proximal end, and a plurality of intermediate steps having incrementally increasing diameters disposed between the first and terminal steps. The step drill bit also includes a plurality of cutting edges each disposed along one of the plurality of steps. Each edge defines a helix angle and a radial rake angle. The radial rake angle and the helix angle of the cutting edge at the terminal step is greater than the radial rake angle and the helix angle of the cutting edge at the first step.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/387,621, filed Apr. 18, 2019, now U.S. Pat. No. 11,273,501, whichclaims priority to U.S. Provisional Patent Application No. 62/662,857,filed Apr. 26, 2018, the entire contents of which are incorporated byreference herein.

BACKGROUND

The present invention relates to power tool accessories. Morespecifically, the present invention relates to step drill bits.

Step drill bits are used in a variety of applications and industrieswhere a user may need to drill holes through a thin-walled work piece. Astep drill bit allows a user to drill holes in a progressive range ofsizes with a single bit. Step drill bits can be coupled to a power toolsuch as a drill or an impact driver. In cases where a step drill bit isused with an impact driver, a cutting edge of the step drill edge ismore prone to chipping.

SUMMARY

In one embodiment, the invention provides a drill bit including a shankextending along a bit axis and a body with a proximal end adjacent theshank and a distal end opposite the proximal end. The body defines aplurality of axially stacked, progressively sized steps including afirst step at the distal end and a terminal step at the proximal end.The drill bit also includes a flute in the body. The flute defines anelongated groove that extends from the distal end to the proximal end.The drill bit further includes a plurality of cutting edges formed inthe body. Each cutting edge is disposed along one of the plurality ofsteps and defines a helix angle and a rake angle. The helix angle of thecutting edge at the terminal step is greater than the helix angle of thecutting edge at the first step. A ratio of the helix angle to the rakeangle of the cutting edge at the first step is in a range from 0.5 to2.4, and a ratio of the helix angle to the rake angle of the cuttingedge at the terminal step is in a range of 0.9 to 1.7.

In another embodiment, the invention provides a drill bit including ashank extending along a bit axis and a body with a proximal end adjacentthe shank and a distal end opposite the proximal end. The body defines aplurality of axially stacked, progressively sized steps including afirst step at the distal end and a terminal step at the proximal end.The drill bit also includes a flute in the body. The flute defines anelongated groove that extends from the distal end to the proximal end.The drill bit further includes a plurality of cutting edges formed inthe body. Each cutting edge is disposed along one of the plurality ofsteps and defines a helix angle and a rake angle. The helix angle of thecutting edge at the terminal step is greater than the helix angle of thecutting edge at the first step. The rake angle of the cutting edge atthe terminal step is greater than the rake angle of the cutting edge atthe first step.

In another embodiment, the invention provides a drill bit including ashank extending along a bit axis and a body with a proximal end adjacentthe shank and a distal end opposite the proximal end. The body defines aplurality of axially stacked, progressively sized steps including afirst step at the distal end and a terminal step at the proximal end.The drill bit also includes at least one flute in the body. Each flutedefines an elongated groove that extends from the distal end to theproximal end. The drill bit further includes a plurality of cuttingedges formed in the body. Each cutting edge is disposed along one of theplurality of steps and defines a helix angle and a rake angle. The helixangle of the cutting edge at the terminal step increases by at least 70percent relative to the helix angle of the cutting edge at the firststep. The rake angle of the cutting edge at the terminal step increasesby at least 40 percent relative to the rake angle of the cutting edge atthe first step.

Other aspects of the present subject matter will become apparent byconsideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a step drill bit according to one embodiment ofthe invention.

FIG. 2 is another side view of the step drill bit of FIG. 1 rotated 90degrees.

FIG. 3 is a first perspective view of the step drill bit of FIG. 1 .

FIG. 4 is a second perspective view of the step drill bit of FIG. 1 .

FIG. 5 is a top view of the step drill bit of FIG. 1 .

FIG. 6 is a cross section view of the step drill bit of FIG. 1 takenalong section line 6-6.

FIG. 7 is a detailed view of section 7 of the step drill bit of FIG. 1

FIG. 8 is a side view of a step drill bit according to anotherembodiment of the invention.

FIG. 9 is another side view of the step drill bit of FIG. 8 rotated 90degrees.

FIG. 10 is a side view of a step drill bit according to anotherembodiment of the invention.

FIG. 11 is another side view of the step drill bit of FIG. 10 rotated 90degrees.

Before any embodiments are explained in detail, it is to be understoodthat the present subject matter is not limited in its application to thedetails of construction and the arrangement of components set forth inthe following description or illustrated in the following drawings. Thepresent subject matter is capable of other embodiments and of beingpracticed or of being carried out in various ways. As used herein, theterm “approximately” refers to values within a rounding range andmanufacturing tolerances of the listed value.

DETAILED DESCRIPTION

FIGS. 1-7 illustrate a step drill bit 10 for use with a power tool, suchas, for example, a drill, a driver drill, an impact driver, and thelike. The step drill bit 10 may be used to cut holes or drill into aworkpiece such as sheet metal, wood, and the like. The illustrated stepdrill bit 10 comes in a variety of sizes that correspond to the type ofhole to be drilled.

FIGS. 1 and 2 illustrate a step drill bit 10 including a shank 12, atransition portion 16, and a body 18. The shank 12 is configured toengage a power tool for rotation of the step drill bit 10 about a bitaxis 14. The illustrated bit axis 14 is a central longitudinal axis ofthe step drill bit 10. The transition portion 16 is defined between theshank 12 and the body 18. The body 18 includes a first or proximate end19A adjacent the shank 12 and a second or distal end 19B opposite theproximate end 19A. The body 18 defines axially stacked, progressivelysized steps 20A-20M between a bit tip 21 and the transition portion 16.The steps 20A-20M are axially stacked in that the steps 20A-20M arecoaxially arranged along the bit axis 14. In addition, the steps 20A-20Mare progressively sized in that the steps 20A-20M incrementally increasein size (e.g., diameter) from the bit tip 21, or the distal end 19B, ofthe body 18 to the transition portion 16, or proximate end 19A. In theillustrated embodiment, the body 18 includes thirteen steps 20A-20M. Inother embodiments, the body 18 may include fewer or more steps.

With continued reference to FIG. 1 , the shank 12 may be a hex-shapedshaft, a round shaped shank, a 3-flat type shank, or any other shank 12that is configured to be coupled to a power tool. In the illustratedembodiment, the shank 12 has a diameter between of approximately 0.125inches to 0.3 inches. In some embodiments, an indication band may belocated on the shank 12. The indication band may indicate to a user thetype of the step drill bit 10. In further embodiments, the step drillbit 10 may include laser engravings that indicate to a user the size ortype of step drill bit. The indication band may be a variety of colorssuch as red, green, blue, purple, orange, yellow, etc.

As shown in FIG. 2 , each of the steps 20A-20M of the body 18 has a stepheight 56A-56M. The step heights 56A-56M are not required to be the samefor all steps. For example, in some embodiments, steps that correspondto commonly-used drill diameters (e.g., 0.5 inch, 0.75 inch, etc.) mayhave larger heights to allow a user to more easily control the stepdrill bit 10 to stop at those corresponding steps. The illustrated stepsinclude a first step 20A at the distal end 19B of the body 18 and aterminal step 20M coupled to the transition portion 16. In theillustrated embodiment, the first step 20A has a diameter ofapproximately 0.125 inches, and the terminal step 20M has a diameter ofapproximately 0.505 inches. The diameter of the terminal step 20Mdefines a max diameter of the step drill bit 10. The diameter of theterminal step 20M is greater than a diameter of the transition portion16. The intermediate steps 20B-20L located between the first andterminal steps 20A, 20M have incrementally increasing diameters withinthe range of 0.125 inches and 0.505 inches. In other embodiments, asfurther described below, the body 18 may include fewer or more steps,and/or each step 20A-20M may have a different diameter.

With reference back to FIG. 1 , a step chamfer 58 is formed between eachpair of adjacent steps 20A-20M. The step chamfer 58 connects twoadjacent steps at a ramp angle 60 to provide a smoother transitionbetween the adjacent steps. The ramp angle 60 is measured between asurface of the corresponding step chamfer 58 and a plane 61 extendingperpendicular to the bit axis 14. In the illustrated embodiment, theramp angle 60 for all of the step chamfers 58 is between approximately40 degrees and approximately 50 degrees, and more specifically,approximately 45 degrees. In other embodiments, the ramp angle 60 may berelatively larger or smaller, or the step chamfers 58 may be omitted. Inthe illustrated embodiment, the ramp angle 60 is the same for all thesteps 20. In other embodiments, the ramp angle 60 may vary per step 20

With reference back to FIG. 2 , the bit tip 21 has a primary tip angle22 measured through the bit axis 14. In some embodiments, the tip angle22 is between approximately 130 degrees and approximately 140 degrees.In the illustrated embodiment, the tip angle 22 is approximately 135degrees. As shown in FIG. 5 , the bit tip 21 includes a dual-relief tiphaving two first chisel surfaces 24 and two second chisel surfaces 26.Each first chisel surface 24 is located on an opposite side of a chiseledge 28 of the bit tip 21 from a corresponding second chisel surface 26.The bit tip 21 defines a chisel width 30 measured between cutting edges32 of the chisel surfaces 24, 26. In some embodiments, the chisel width30 is between approximately 0.02 inches and 0.03 inches. In otherembodiments, the chisel width 30 is between approximately 0.022 inchesand approximately 0.028 inches. In the illustrated embodiment, thechisel width 30 is approximately 0.025 inches. In further embodiments,the primary tip angle 22 and/or the chisel width 30 may be relativelylarger or smaller.

Referring to FIGS. 3-4 , the body 18 defines two body flutes 46 disposedon diametrically opposite sides of the bit axis 14. Each of the flutes46 is helically wrapped around the body 18 and extends from the firststep 20A to the transition portion 16. Each flute 46 defines a groove 48between two edges 50A-B in the body 18. In the illustrated embodiment,the step drill bit 10 includes two flutes 46. In other embodiments, thestep drill bit 10 may include a single flute 46 or more than two flutes46.

With continued reference to FIGS. 3-4 , each of the steps 20A-20Mincludes a leading cutting edge (e.g., cutting edges 64A labeled in FIG.3 , cutting edge 64C labeled in FIGS. 3 and 4 , and cutting edge 64Mlabeled in FIG. 6 ). The leading cutting edges are defined on the edge50A of the groove 48 of the flute 46. Each cutting edge forms a rakeangle (i.e., a radial rake angle) between the outer periphery of arespective step 20A-20M and the surface of the groove 48 (e.g., rakeangle 66C labeled in FIG. 4 and rake angle 66M labeled in FIG. 6 ). Inthe illustrated embodiment, the rake angle at the first step 20A isapproximately 5 degrees and the rake angle at the terminal step 20M isapproximately 25 degrees. The intermediate steps 20B-20L haveincrementally increasing rake angles that are within a range from 5degrees and 25 degrees. In some embodiments, the increase to the rakeangles may be linear or non-linear. In other embodiments, the rakeangles may be smaller than 5 degrees or bigger than 25 degrees.Additionally, each cutting edge defines a helix angle that is measuredbetween the cutting edge 64A-64M and the bit axis 14 (e.g., helix 68Clabeled in FIG. 3 ). In the illustrated embodiment, the helix angle atthe first step 20A is approximately 12 degrees and the helix angle atthe terminal step 20M is approximately 22 degrees. The intermediatesteps 20B-20L have incrementally increasing helix angles that are withina range from 12 degrees to 22 degrees. In some embodiments, the increaseto the helix angles may be linear or non-linear. In other embodiments,the helix angles may be smaller than 12 degrees or larger than 22degrees. In the illustrated embodiment, a ratio between the helix angleand the rake angle for the first step 20A is approximately 2.4, and theratio between the helix angle and the rake angle for the terminal step20M is approximately 0.9.

With reference to FIG. 6 , a core depth 52 of the step drill bit 10 isdefined between the two flutes 46 of the body 18 extending through thebit axis 14. The core depth 52 increases from the distal end 19B of thebody 18 to the proximal end 19B of the body. As such, the core depth 52increases every step 20A-20M from the first step 20A to the terminalstep 20M. The core depth 52 may be in a range from 0.05 inches to 0.6inches.

The thirteen steps 20A-20M of the step drill bit 10 each include threetypes of reliefs: an axial relief 74 (FIG. 7 ), a diametral relief 76(FIG. 7 ), and a radial relief 78 (FIG. 5 ). As shown in FIG. 7 , theaxial relief 74 of each step 20A-20M is the amount by which an upperedge 80 of the step (i.e., the edge of the step closest to the distalend of the body 18) translates along the bit axis 14 toward the distalend as the upper edge 80 nears a leading cutting edge 64C of the step(i.e., the edge of the step at the body flute 46). In some embodiments,the axial relief 74 of each step 20A-20M is between approximately 0.002inches and approximately 0.01 inches. In the illustrated embodiment, theaxial relief 74 is approximately 0.005 inches. In other embodiments, theaxial relief 74 may be relatively larger or smaller.

With continued reference to FIG. 7 , the diametral relief 76 of eachstep 20A-20M is the amount by which an outer circumferential surface 84of the step tapers radially inward or outward along the bit axis 14. Inthe illustrated embodiment, the diametral relief 76 of each step 20A-20Mis between approximately −1 degree and approximately 1 degree. In someembodiments, the diametral relief 76 may be omitted (i.e., may be 0degrees). In other embodiments, the diametral relief 76 may be arelatively greater positive degree or a relatively greater negativedegree.

With reference to FIG. 5 , the radial relief 78 is the amount by which aradius 86 of the steps 20A-20M decreases as the outer surface of thestep 20A-20M moves away from the leading edge 82. More particularly, aconstant diameter circle 88 is illustrated in FIG. 5 in broken lines,representing the nominal diameter of the third step 201. The radialrelief 78 continuously increases along a radial relief angle 34 from theleading edge 82 of the step to a point at which the radial relief 78 hasreached its maximum value or amount. As used herein, the “radial relief”is the maximum amount that the radius 86 of the step 201 decreasesradially inward from the nominal diameter 88. In some embodiments, theradial relief 78 of each step 20A-20M is between approximately 0.002inches and approximately 0.01 inches. In the illustrated embodiment, theradial relief 78 is approximately 0.005 inches. In addition, the radialrelief angle 34 of each step 20A-20M is between approximately 40 degreesand approximately 50 degrees from the leading edge 82. In theillustrated embodiment, the radial relief angle 34 is approximately 45degrees. In other embodiments, the radial relief 78 and/or the radialrelief angle 34 may be relatively larger or smaller.

FIGS. 8-9 illustrate a step drill bit 110 according to anotherembodiment of the invention. The step drill bit 110 includes featuressimilar to the step drill bit 10 of FIGS. 1-7 , and like features havebeen given like reference numbers plus 100. The step drill bit 110 mayinclude any combination of features, dimensions, or range of dimensionsfrom the preceding or subsequent embodiments, but only features of thestep drill bit 110 not yet discussed with respect to the previousembodiment are detailed below.

The step drill bit 110 includes two flutes 146 and twelve axiallystacked, progressively sized steps 120A-120L. A first step 120A has adiameter of approximately 0.188 inches, and a terminal step 120L has adiameter of approximately 0.88 inches. Each of the steps 120A-120Linclude a leading cutting edge 164A-164L. Each cutting edge 164A-164Lforms a rake angle (e.g., rake angle 166G labeled in FIG. 9 ) betweenthe outer periphery of a respective step 120A-120L and the surface of aflute 146 and a helix angle (e.g., helix angle 1681 labeled in FIG. 8 )that is measured between the cutting edge 164A-164L and a bit axis 114.

The rake angle at the first step 120A is approximately 5 degrees, andthe rake angle at the terminal step 20L is approximately 18 degrees. Theintermediate steps 120B-120K have incrementally increasing rake anglesthat are within a range from 5 degrees and 18 degrees. In someembodiments, the increase to the rake angles may be linear ornon-linear. In other embodiments, the rake angles may be smaller than 5degrees or bigger than 18 degrees.

The helix angle at the first step 120A is approximately 7 degrees, andthe helix angle at the terminal step 120L is approximately 29 degrees.The intermediate steps 120B-220K have incrementally increasing helixangles that are within a range from 7 degrees to 29 degrees. In someembodiments, the increase to the helix angles may be linear ornon-linear. In other embodiments, the helix angles may be smaller than 7degrees or larger than 29 degrees. In the illustrated embodiment, aratio between the helix angle and the rake angle for the first step 120Ais approximately 1.4, and the ratio between the helix angle and the rakeangle for the terminal step 120L is approximately 1.6.

FIGS. 10-11 illustrate a step drill bit 210 according to anotherembodiment of the invention. The step drill bit 210 includes featuressimilar to the step drill bit 10 of FIGS. 1-7 , and like features havebeen given like reference numbers plus 100. The step drill bit 210 mayinclude any combination of features, dimensions, or range of dimensionsfrom the preceding or subsequent embodiments, but only features of thestep drill bit 210 not yet discussed with respect to the previousembodiment are detailed below.

The step drill bit 210 includes two flutes 246 and twenty axiallystacked, progressively sized steps 220A-220T. A first step 220A has adiameter of approximately 0.188 inches, and a terminal step 220T has adiameter of approximately 1.13 inches. Each of the steps 220A-220Tincludes a leading cutting edge 264A-264T. Each cutting edge 264A-264Tforms a rake angle (e.g., rake angle 266L labeled in FIG. 10 ) betweenthe outer periphery of a respective step 220A-220T and the surface of aflute 246 and a helix angle (e.g., helix angle 268L labeled in FIG. 11 )that is measured between the cutting edge 264A-264T and a bit axis 214.

The rake angle at the first step 220A is approximately 20 degrees, andthe rake angle at the terminal step 20L is approximately 12 degrees. Theintermediate steps 220B-220S have incrementally decreasing rake anglesthat are within a range from 12 degrees and 20 degrees. In someembodiments, the decrease to the rake angles may be linear ornon-linear. In other embodiments, the rake angles may be smaller than 12degrees or bigger than 20 degrees.

The helix angle at the first step 220A is approximately 10 degrees, andthe helix angle at the terminal step 220T is approximately 18 degrees.The intermediate steps 220B-220S have incrementally increasing helixangles that are within a range from 10 degrees to 18 degrees. In someembodiments, the increase to the helix angles may be linear ornon-linear. In other embodiments, the helix angles may be smaller than10 degrees or larger than 18 degrees. In the illustrated embodiment, aratio between the helix angle and the rake angle for the first step 220Ais approximately 0.5, and the ratio between the helix angle and the rakeangle for the terminal step 220T is approximately 1.5.

As mentioned above, the step drill bit 10, 110, 210 may include anynumber of steps 20, 120, 220 with any range of diameters thatincrementally increase from the first step 20 to the terminal step 20.As shown in Table 1 below, for a particular minimum diameter to maximumdiameter and number of steps of a step drill bit 10, 110, 210 the ratiobetween the first step 20 and the terminal step 20 may vary depending onthe type of step drill bit 10, 110, 210.

Helix Angle/ Min. Max. Number Rake Angle Diameter Diameter of FirstTerminal (in) (in) Steps Step Step 0.125 0.505 13 2.4 0.9 0.188 0.505 62.0 1.2 0.188 0.755 10 1.4 1.2 0.188 0.88 12 1.4 1.6 0.188 1.005 14 1.21.7 0.188 1.13 20 0.5 1.5 0.162 0.47 9 1.2 0.9 0.162 0.47 5 1.2 0.90.162 0.79 9 0.7 1.3 0.162 1.186 19 0.7 1.0

Additionally, for a particular maximum diameter of a drill bit 10, 110,210 the percent the rake angle and the helix angle change from the firststep 20 and the terminal step 20 may vary depending on the type of stepdrill bit 10, 110, 120. Table 2 below shows the percent of changebetween the first step 20 and the terminal step 20. For example, thehelix angle of the cutting edge at the terminal step of a drill bit 10,110, 210 may increase by at least 70 percent relative to the helix angleof the cutting edge at the first step of the drill bit 10, 110, 210. Therake angle of the cutting edge at the terminal step of the drill bit 10,110, 210 may increase by at least 40 percent relative to the rake angleof the cutting edge at the first step of the drill bit 10, 110, 210.Preferably, the helix angle increases from the first step to theterminal step within a range between 70 and 450 percent, and the rakeangle increases from the first step to the terminal step within a rangebetween 40 and 500 percent.

In some embodiments, the percent change may be positive indicating therake angle or helix angle increased from the first step 20 to theterminal step 20. In other embodiments, the percent change may benegative indicating the rake angle or helix angle decreased from thefirst step 20 to the terminal step 20.

Helix Angle Rake Angle Max. First Terminal Percent First TerminalPercent Diameter Step Step change Step Step Change (in) (deg) (deg) (%)(deg) (deg) (%) 0.5 12 22 83 5 25 400 0.5 10 24.75 148 5 20 300 0.75 737 429 5 30 500 0.88 7 29 314 5 18 260 1.00 12 26 117 10 15 50 1.13 1018 80 20 12 −40 0.47 12 22 83 10 25 150 0.47 12 22 83 10 25 150 0.79 732 357 10 25 150 1.18 10 18 80 15 18 20

In some embodiments, the step drill bit 10, 110, 210 may include laseretchings on an outside surface of the steps 20 indicating to a user thediameter of a hole the particular step 20 would drill in a workpiece. Infurther embodiments, the step drill bit 10,110, 210 may be coated in aprotective coating with properties that increase wear resistance. Forexample, the step drill bit 10, 110, 210 may be coated in a titaniumaluminum nitride coating (i.e., TiAlN) that is 2-5 microns thick.Alternatively, the step drill bit 10, 110, 210 may be coated in atitanium nitride coating (i.e., TiN) that is 2-5 microns thick. Further,the step drill bit 10,110, 210 may be coated in an aluminum titaniumnitride (i.e., AlTiN). In addition, step drill bits 10, 110, 210 withTiAlN, TiN, or AlTiN coatings may be heat treated and tempered. In otherembodiments, the step drill bit may only be heat treated and tempered.

Optimizing the ratio between a helix angle and a rake angle on thecutting edges of steps on a step drill bit advantageously increases thespeed and life of the step drill bit. A helix angle that is too high ata distal end of the step drill bit will provide poor hole quality. Ahelix angle that is too low at a distal end will cause the step drillbit to be slower during operation. A helix angle that is too high at theproximate end of a step drill bit will jam during operation. A helixangle that is too low at the proximate end of a step drill bit will beslower during operation and lessen the life of the step drill bit. Arake angle that is too high at the front and back of the step drill bitwill cause the cutting edge to chip. A rake angle that is too low at thefront and back of the step drill bit will be slow and produce poor holequality. Thus, providing a step drill bit with a ratio between the helixangle and the rake angle between 0.5 and 2.4, ensures that the stepdrill bit cuts workpieces in a fast and clean manner while prolongingthe life. Additionally, adding a wear resistance coating to the stepdrill bit will prolong the life of the step drill bit further.

Various features and advantages of the invention are set forth in thefollowing claims.

What is claimed is:
 1. A step drill bit comprising: a shank extendingalong a bit axis; a body having a proximal end adjacent the shank and adistal end opposite the proximal end, the body defining a plurality ofaxially stacked, progressively sized steps including a first step at thedistal end, a terminal step at the proximal end, and a plurality ofintermediate steps having incrementally increasing diameters disposedbetween the first and terminal steps; a flute in the body extending fromthe distal end to the proximal end; and a plurality of cutting edgesformed in the body, each cutting edge disposed along one of theplurality of steps, each cutting edge defining a helix angle and aradial rake angle; wherein the helix angle of the cutting edge at theterminal step is greater than the helix angle of the cutting edge at thefirst step; and wherein the radial rake angle of the cutting edge at theterminal step is greater than the radial rake angle of the cutting edgeat the first step.
 2. The step drill bit of claim 1, wherein theplurality of intermediate steps includes at least four steps.
 3. Thestep drill bit of claim 1, wherein a diameter of the terminal stepdefines a max diameter of the drill bit.
 4. The step drill bit of claim3, further comprising a transition portion between the body and theshank, the transition portion having a diameter that is smaller than thediameter of the terminal step.
 5. The step drill bit of claim 1, whereinthe flute is a first flute, and the drill bit further comprises a secondflute on a diametrically opposite side of the bit axis from the firstflute.
 6. The step drill bit of claim 5, wherein the body includes acore depth defined between the first and second flutes and extendingthrough the bit axis, the core depth increasing from the first step tothe terminal step.
 7. The step drill bit of claim 1, wherein adjacentsteps of the plurality of steps are connected by a step chamfer.
 8. Thestep drill bit of claim 7, wherein each step chamfer defines a rampangle between a surface of the step chamfer and a plane extendingperpendicular to the bit axis, each ramp angle is between approximately40 degrees and approximately 50 degrees.
 9. The step drill bit of claim1, wherein the body includes a bit tip adjacent the first step.
 10. Thestep drill bit of claim 9, wherein the bit tip includes a primary tipangle measured through the bit axis between approximately 130 degreesand approximately 140 degrees.
 11. The step drill bit of claim 1,wherein each helix angle is between approximately 5 degrees andapproximately 30 degrees.
 12. The step drill bit of claim 11, whereineach radial rake angle is between approximately 5 degrees andapproximately 35 degrees.
 13. A step drill bit comprising: a shankextending along a bit axis; a body having a proximal end adjacent theshank and a distal end opposite the proximal end, the body defining aplurality of axially stacked, progressively sized steps including afirst step at the distal end, a terminal step at the proximal end, and aplurality of intermediate steps having incrementally increasingdiameters disposed between the first and terminal steps; a flute in thebody extending from the distal end to the proximal end; and a pluralityof cutting edges formed in the body, each cutting edge disposed alongone of the plurality of steps, each cutting edge defining a helix angleand a radial rake angle; wherein the radial rake angle of the cuttingedge at the terminal step is greater than the radial rake angle of thecutting edge at the first step, and wherein the radial rake angles ofthe cutting edges incrementally increase from a first step of theplurality of intermediate steps to a second step of the plurality ofintermediate steps, and from the second step of the plurality ofintermediate steps to a third step of the plurality of intermediatesteps.
 14. The step drill bit of claim 13, wherein each radial rakeangle is between approximately 5 degrees and approximately 35 degrees.15. The step drill bit of claim 13, wherein the wherein the plurality ofintermediate steps includes at least four steps.
 16. The step drill bitof claim 13, wherein the radial rake angle of the cutting edge at theterminal step increases by at least 40 percent relative to the radialrake angle of the cutting edge at the first step.
 17. A step drill bitcomprising: a shank extending along a bit axis; a body having a proximalend adjacent the shank and a distal end opposite the proximal end, thebody defining a plurality of axially stacked, progressively sized stepsincluding a first step at the distal end, a terminal step at theproximal end, and a plurality of intermediate steps having incrementallyincreasing diameters disposed between the first and terminal steps; aflute in the body extending from the distal end to the proximal end; anda plurality of cutting edges formed in the body, each cutting edgedisposed along one of the plurality of steps, each cutting edge defininga helix angle and a radial rake angle; wherein the helix angle of thecutting edge at the terminal step is greater than the helix angle of thecutting edge at the first step; wherein the helix angles of the cuttingedges incrementally increase from a first step of the plurality ofintermediate steps to a second step of the plurality of intermediatesteps, and from the second step of the plurality of intermediate stepsto a third step of the plurality of intermediate steps.
 18. The stepdrill bit of claim 17, wherein each helix angle is between approximately5 degrees and approximately 30 degrees.
 19. The step drill bit of claim17, wherein the plurality of intermediate steps includes at least foursteps.
 20. The step drill bit of claim 17, wherein the helix angle ofthe cutting edge at the terminal step increases by at least 70 percentrelative to the helix angle of the cutting edge at the first step.